Method for modifying the design of a structural part

ABSTRACT

A method for modifying, in particular optimizing, the design of a component with regard to one or more criteria using a virtual model of the component, having the following steps:  
     a) a virtual model of the component is produced by combination of the component from basic objects with the aid of Boolean operators,  
     b) each basic object is assigned an information element in which attributes of the basic object, in particular parameter values, interval limits and rules, are stored,  
     c) each basic object is decomposed into primitive objects which are combined with aid of Boolean operators, the primitive objects being surfaces or bodies which can be decomposed into rasters,  
     d) each geometrical contact surface or contact line which is produced in the case of the Boolean operation between two or more objects is assigned a connecting element in which information for coordinating the objects is stored,  
     e) the rastering of the primitive objects is performed by a conventional gridding method,  
     f) a modification of the geometrical shape of individual or a group of objects is undertaken, the information of the information elements defining the limits of possible modifications

[0001] The invention relates to a method for modifying, in particularfor optimizing, the design of a component with regard to one or morecriteria using a virtual model of the component.

[0002] The current development processes are developing from stepwisedevelopment towards simultaneous development, the disciplines oftechnical development and analysis being in closer cooperation, andknowledge of all relevant technical disciplines being introduced inearly phases of product development. Simultaneous development is foundto be necessary in order to develop products with improved technologyand of higher quality in a shorter development time, something whichalso leads to reduced costs.

[0003] The probability of the development of better and less expensivecomponents is rising in principle through the application of highperformance analysis tools and the knowledge of experts in the variousfields of engineering science. A possible impediment to success is,however, the normally limited time in which the components have to bedeveloped.

[0004] With this in mind, the multidisciplinary design optimization(MDO) is regarded as an effective method for improving quality andperformance of products in conjunction with reducing costs. This happenschiefly through shortening the evaluation time required overall for adesign cycle, and by creating an automated analysis tool which searchesfor the best solution or performs specific tasks in a limited time.

[0005] Various publications provide a good overview of the state of theart in multidisciplinary design optimization. To name only a few, thereare the articles by Alexandrov edit. [Natalia Alexandrov and M. Y.Hussaini, editors, Multidisciplinary Design Optimization—State of theArt, SIAM 1997], Bartholomew [Peter Bartholomew, The role of MDO withinaerospace design and progress towards an MDO capability; in 7thAIAA/USAF/NASA/ISSIMO Symposium on Multidisciplinary Analysis andOptimization, p. 2157-2165; AIAA, 1998], Kroo [Ilan Kroo; Mdo forlarge-scale design; in Natalia M. Aleandrov and M. Y. Hussaini, editors,Multidisciplinary Design Optimization—State of the Art, pages 22-44;SIAM, 1997], Sobieski and Haftka [Jaroslaw Sobieszczanski-Sobieski andRaphael T. Haftka; Multidisciplinary aerospace design optimization:Survey of recent developments, Conference Paper 96-0711, AIAA, 1996.Presented at the 34th Aerospace Sciences Meeting and Exhibit; Jan.15-18, 1996] and Vanderplaats [G. N. Vanderplaats; Structural designoptimization status and direction; Journal of Aircraft, 36(1):11-20,January-February 1999].

[0006] Sobieski and Haftka distinguish between three categories ofmultidisciplinary design optimization, which place differentrequirements on EDP and organization.

[0007] The first category comprises only a few technical disciplines. Anexpert can process all the required information and all necessaryknowledge.

[0008] The second category comprises all methods which achieve themultidisciplinary object, all the required technical disciplines beingintroduced at a low degree of complexity. This optimization method ismostly applied to the design concept of a system, the analysis toolsbeing used as individual modules. If these methods are applied to tasksin the continuing design process, they are confronted with some of theorganizational challenges set by multidisciplinary design optimization.

[0009] The third category is described as a stage of the challenge interms of computing and organization. In order to permit the analysis ina modular environment, specific techniques, for example, decomposition,approximation and comprehensive sensor technologies are used as tools inorder to organize the modules themselves and the exchange of data.

[0010] Similar classifications are proposed in other publications, forexample by Bartholomew and Kroo. They distinguish between the variousdegrees of complexity and accuracy of the applied analysis programs andthe optimization architecture.

[0011] The publications described above lead to a modular analysisenvironment, something which necessitates the use of decomposition andapproximation techniques in order to be able to solve relatively complexdesign tasks. Kroo explains the necessity to develop the parameterizedgeometry at different degrees of detail and abstraction in order to beable to apply the multidisciplinary optimization to realistic,large-scale design tasks which comprise many disciplines and analysistools from the state of the art.

[0012] In order to permit the fully automated design optimization withthe use of a parameterized geometry at different degrees of detail, thegeometry modelling must be more strongly linked to the rastering.Samareh [Jamshid A. Samareh; Status and future of geometry modelling andgrid generation for design and optimization; Journal of Aircraft,36(1):97-104, January-February 1999] compiles an overview of therequirements to be fulfilled and the problems to be solved in order tocreate such a fully automated geometry model and a rastering method formultidisciplinary optimization applications.

[0013] Another aspect of multidisciplinary design optimization isdiscussed by Wood and Bauer in [Richard M. Wood and Steven X. S. Bauer;A discussion of knowledge based design; Conference Paper 98-4944, AIAA,1998; Presented at the 7th AIAA/USAF/NASA/ISSMO Symposium onMultidisciplinary Analysis and Optimization; Sep. 2-4, 1998]. Wood andBauer point out the need to allow expert knowledge to flow into theoptimization process in order to improve the technology and quality ofthe products. They say that knowledge from previous design cycles mustflow into the early phase of the design process.

[0014] None of the solutions known from the prior art permits acompletely automated design optimization.

[0015] It is an object of the present invention to propose a completelyautomated method for multidisciplinary design optimization of the two-,quasi-three- or three-dimensional component which permits small-scalechanges to be transferred to the complete component.

[0016] A method having the features of claim 1 is proposed according tothe invention.

[0017] The inventive method can be used to modify a component, inparticular to optimize it, by applying modifications to different stagesof details of the component. The first stage is to create a virtualmodel of the component. For this purpose, the component is combined frombasic objects with the aid of solid modelling Boolean operators, thebasic objects being, in particular, surfaces or rotationally symmetricalbodies. Each of the basic objects is assigned an information element inwhich the attributes of the respective basic object, in particularparameter values, interval limits and rules, are stored. Theseattributes determine and delimit the respective basic object.

[0018] It has hereby become possible to render accessible tomultidisciplinary design optimization geometries and/or basic objects towhich knowledge and/or information is allocated.

[0019] Each basic object is then constructed from further basic objectsor one or more primitive objects which are combined with the aid ofBoolean operators. The primitive objects are surfaces or bodies ofdifferent complexity and geometrical multiplicity which can bedecomposed into rasters. Each further basic object or primitive objectcan again be assigned an information element in which the attributes ofthe further basic object or the primitive object, in particularparameter values, interval limits and rules, can be stored. Theseattributes determine and delimit the respective primitive object.

[0020] The Boolean combination of the component from individual basicobjects yields geometrical contact surfaces or contact lines between twoor more objects. The same also holds for the primitive objects. Each ofthese geometrical contact surfaces and contact lines is assigned aconnecting element in which information for coordinating the objects isstored.

[0021] These so-called connecting or coordination elements can also beallocated as additional knowledge to each basic object or primitiveobject in order to obtain a better subdivision into rasterable surfacesin the further process.

[0022] The primitive objects are rastered in the next step, specificallyby a conventional griding method.

[0023] The modification of the component can be undertaken subsequently.This is performed by modifying individual or a group of objects, theinformation of the information elements defining the limits of possiblemodifications, the connecting elements defining the coordination of theobjects. Customary raster techniques are applied in this case.

[0024] The proposed model is a feature-based geometry model whichpermits multidisciplinary optimization in different degrees of detail.It uses an object-oriented access in order to produce the geometry andto integrate all the information required during the design process. Thegeometry at different degrees of detail permits starting with atwo-dimensional geometry, then with rotationally symmetrical orstretched bodies, and finally with a realistic, three-dimensionalgeometry.

[0025] Advantageous refinements of the inventive method are described inthe subclaims.

[0026] The basic objects can be constructed from one or more furtherbasic objects or primitive objects which can be combined by Booleanoperators. Each basic object is again assigned an information element inthis case, in which attributes of the basic object, in particularparameter values, interval limits and rules, are stored. Eachgeometrical contact surface or contact line which is produced in thecase of the Boolean operation between two or more objects is assigned aconnecting element in which information for coordinating the objects isstored.

[0027] The primitive objects can also be constructed from one or morefurther primitive objects, as a result of which it is possible to modifythe degree of detail or the degree of construction of the model can bemodified.

[0028] The primitive objects can, in turn, be combined by Booleanoperators. They can be assigned in each case an information element inwhich attributes of the primitive object, in particular parametervalues, interval limits and rules, are stored. Each geometrical contactsurface or contact line which is produced in the case of the Booleanoperation between two or more objects can be assigned a connectingelement in which information for coordinating the objects is stored.

[0029] The modification of the geometrical shape is preferably performedexclusively or predominantly on the lowest object plane, that is to saythe primitive objects, it being possible to raster the objects to bemodified.

[0030] The inventive method proposed permits the multidisciplinaryoptimization of a component by modifying the degree of detail. Eachtechnical discipline can start with the optimization at the stageoptimum for it. The details of this design can be changed during theoptimization process without the need for a complete change to thestructure and topology of the previously designed geometry.

[0031] All the information required in later design steps can be takenfrom the information elements assigned to the individual objects, or bederived from the information. The information contained can be employedor passed to other tools.

[0032] The inventive modification method is preferably applied tooptimize a component. It is preferably used after termination of thebasic conception with a lower level of detail, and increases the varietyof detail and the complexity of the topology as the process progresses.

[0033] The degree of the level of detail of the geometry of the modelcan be modified by changing the type of the primitive objects, by addingfurther objects to the preceding model, that is to say the latter isconstructed from further basic objects and/or primitive objects.

[0034] A feature of the component can be represented by combining aprimitive object with an information element which contains attributesof the object. These can be, in particular, parameter values, intervallimits or rules. The rules reflect the knowledge of a person skilled inthe art of the respective fields. It is thus therefore possible todefine a feature of the component as a geometrical object which containsall the specific information which is required to determine and todelimit the geometry.

[0035] It is also possible to derive from the information stored in theinformation element further information and rules which are required inlater design phases.

[0036] In order to render automated geometry modelling and rasteringpossible, it is desirable to maintain the principle features of eachprimitive object during the assembly of the topology of the overallcomponent. The modelling technique is expanded for this purpose bycreating additional curves or surfaces at the points at which objectsare connected to one another or separated from one another.

[0037] These additional curves or surfaces are termed connectingelements. The connecting elements are used in order to decompose thegeometry, which is constructed from rasterable constituents, into theserasterable constituents. These elements can both be producedautomatically during the modelling with the aid of Boolean operators,and be allocated to each object as additional knowledge. It is then easyto produce a raster for the rasterable primitive objects.

[0038] Boolean operators produce an object which comprises two or moreprimitive objects and one or more connecting elements between theprimitive objects. Which type of object is selected for the primitiveobject depends on the degree of detail. With each further combination ofobjects, the degree of assembly and thus the degree of detail isincreased.

[0039] Each connecting element includes curves or surfaces which cut theprimitive objects such that they do not overlap, but meet preciselyalong this curve or surface. By using this technique, the topology ofeach primitive object can remain substantially the same during theoptimization process. The production of the connecting elementscorresponds to the customary raster methods, in which specificconnecting conditions are determined for each object.

[0040] In another version of the inventive method, the Booleanoperations are combined with an optional generation of intersection setsof neighbouring objects which are introduced into the connectingelement. These intersection sets are created where the two objectsintersect. The connecting elements then contain information on possibleconnecting surfaces or connecting lines between neighbouring objects.The connecting elements can then be positioned for the rastering suchthat they obey as well as possible the rules for producing rasters.

[0041] The primitive objects are preferably standardized, rasterableparts such as triangles, rectangles, pentagons, tetrahedra, pentahedraor hexahedra.

[0042] The primitive objects are preferably produced from surfaces orbodies which use lower geometrical objects, and which are combined withthe aid of Boolean operators or by rotation, stitching or stretching.Primitive objects of the lowest degree of detail are objects such ascircular or rectangular surfaces or bodies. The degree of detail growsthrough the use of objects such as B-spline curves or B-spline surfacesin order to describe the contours or surfaces. The degree of detail ischaracterized by the degree of the geometrical variety. If the number ofthe parameters rises, the objects become more general and the variety ofgeometrical shapes rises.

[0043] The resulting primitive objects are preferably standardized. Theyhave the same input and output parameters, in order to permit a simpleexchange between primitive objects of different degrees of detail.

[0044] An automated rastering is rendered possible by the assembly ofrasterable primitive objects and the insertion of the connectingelements. The production of the connecting elements falls back onknowledge from the decomposition of geometry using the finite elementmethod.

[0045] The actual rastering by a commercially available raster generatorcan be preceded by a preparatory step which makes available the datawhich are required by the raster generator.

[0046] Geometrical information such as, for example vertices, corners,surfaces, bodies, and specific raster information such as, for example,the number of elements, the type of the elements, the number of nodes,can be made available in the preparatory step. The entire geometry isdecomposed at the connecting elements in the case of the method ofrastering preferably used.

[0047] The result is individual surfaces for the production of atwo-dimensional raster, or individual bodies for the production of athree-dimensional raster.

[0048] The advantage of the joining of geometrical modelling andrastering in one system is the high degree of accuracy in the geometry,which is then transferred to a commercially available raster generator.Processes such as the connection of edges which adjoin one another attheir end points, the filtering out of corners which are shorter than aprescribed tolerance, or the closing of gaps between edges, can becarried out by using the information from the geometrical model.

[0049] Boolean operations which are applied during the production of thegeometrical model can cause a change in the contours of the originalprimitive objects. The contour edges can be shortened, or new edges canbe added. The recognition of which edges can be connected is therebyimplemented. Both the raster surface or the raster body, and the edgesof surfaces which belong to the sides of an element can be filtered outby means of this recognition.

[0050] In addition to this recognition process, it is possible to carryout other operations such as, for example, filtering and closing edges.All the information used for commercial raster generation can be derivedfrom the objects recognized.

[0051] Additional information which is relevant for the production ofrasters can be input in to the module or determined during the rasterproduction.

[0052] The production of connecting curves between two objects isexplained in more detail below with the aid of FIGS. 1 to 3:

[0053] FIGS. 1 to 3 show the production of connecting curves forsurfaces. The method is the same for bodies, except that curves are usedinstead of points, and surfaces are used instead of curves in order toproduce the connecting surfaces.

[0054]FIG. 1 shows the production of a connecting curve between twosurfaces.

[0055] If a body is entirely extracted from another body, the connectingcurves are either developed between vertices or corners of the body,FIG. 2, or between the two contours at the point with the minimumdistance from the opposite corners or surfaces, FIG. 3.

[0056] The invention is explained in more detail below with the aid of aturbine wheel and with reference to FIGS. 4 to 7:

[0057] The development of the geometry begins with two-dimensionalobjects, applies rotation operators or stretch operators, and results ina realistic, three-dimensional rendition of the turbine wheel. It ispossible in principle to use four-sided surfaces to describe atwo-dimensional rendition of the rotor component. Two methods are usedto parameterize the contours of these four-sided surfaces. The aim ofthis parameterization is to obtain a great variety of shapes while usingas few parameters as possible.

[0058] Reference points or reference curves are used as input variablesin both methods. The input variables are used as output geometries orfinal geometries and/or to position and orientate the primitive objects.These input variables are used in order to increase the accuracy whentwo objects are connected along a common curve. The differences betweenthe two methods reside in the way in which the contours are produced.One type of primitive objects develops the contour by producing thecontour curve directly (FIG. 4A). The second type produces the contourby defining a skeleton together with specification of a thicknessdistribution for developing the contour curve (FIG. 4B).

[0059] The feature-based geometrical model of a turbine wheel is appliedto an integrally produced rotor stage of a high pressure compressor. Thegeometry firstly has a fictional contour and is not yet analysed oroptimized.

[0060] A possible decomposition of a turbine wheel is illustrated inFIG. 5. The bold points mean that these basic objects are optional andinclude zero or more objects. The basic objects are blades, trunk andshaft. Each basic comprises one or more primitive objects of whichdifferent types can be present, and which can be exchanged withoutchanging the structure of the design. For example, the flange is a basicobject which can have various topologies such as, for example, a flangefor welding or for assembly. If the type of this basic object ismodified, this does not change the structure of the rotor disc, but onlythe topology.

[0061] The geometry of the rotor disc is illustrated in FIG. 6 invarious degrees of detail. The primitive objects are quadrangularobjects which are connected in order to produce the contour depicted.The primitive objects illustrated in FIG. 4A are used for all theobjects which illustrate the trunk and the flanges. The blades areproduced using a type in accordance with FIG. 4B, the contours beingdescribed by a skeleton with a thickness distribution.

[0062] In general, optimization can begin with specific parts or withthe complete geometry. This can be performed by considering only thoseparameter sets which influence these parts, or by considering all theparameters. Likewise, it is possible to carry out optimization using thedifferent degrees of detail or assembly. For a primitive object, thisdegree can be modified with regard to a specific part of the geometry bymodifying the details of the primitive objects or by modifying thedegree of assembly of the basic object. Automatic rastering can becarried out on each stage, and analysis can be started.

[0063] The advantages of the assembly of the geometry and retaining themain characteristics of the primitive objects through the introductionof connecting elements are that a consistent raster can be maintainedduring the optimization and the change in the degree of detail orassembly.

[0064] The finite element raster produced for a rotor disc isillustrated in FIG. 7. The raster remains substantially unmodified whenthe degree of detail or the position of primitive objects is modified,since these changes do not influence the main structure of the assembledgeometry. When more objects are added and the degree of assembly rises,the preceding topology is changed to a minimum extent, and the precedingnetwork can remain substantially unmodified. This may be seen at thetransition between the (connecting) arms and the trunk. The maincharacteristics of the trunk are retained when two (connecting) arms arepresent or are added.

1. Method for modifying, in particular for optimizing, the design of acomponent with regard to one or more criteria using a virtual model ofthe component, having the following steps: a) a virtual model of thecomponent is produced by combination of the component from basic objectswith the aid of Boolean operators, b) each basic object is assigned aninformation element in which attributes of the basic object, inparticular parameter values, interval limits and rules, are stored, c)each basic object is constructed from primitive objects which arecombined with aid of Boolean operators, the primitive objects beingsurfaces or bodies which can be decomposed into rasters, d) eachgeometrical contact surface or contact line which is produced in thecase of the Boolean operation between two or more objects is assigned aconnecting element in which information for coordinating the objects isstored, e) the rastering of the primitive objects is performed by aconventional gridding method, f) a modification of the geometrical shapeof individual or a group of objects is undertaken, the information ofthe information elements defining the limits of possible modifications.2. Method according to claim 1, characterized in that the basic objectsare constructed from one or more further basic objects which arecombined by Boolean operators, and which are assigned in each case aninformation element in which attributes of the basic object, inparticular parameter values, interval limits and rules, are stored, andeach geometrical contact surface or contact line which is produced inthe case of the Boolean operation between two or more objects beingassigned a connecting element in which information for coordinating theobjects is stored.
 3. Method according to claim 1 or 2, characterized inthat the primitive objects are constructed from one or more furtherprimitive objects which are combined by Boolean operators, and which areassigned in each case an information element in which attributes of theprimitive object, in particular parameter values, interval limits andrules, are stored, and each geometrical contact surface or contact linewhich is produced in the case of the Boolean operation between two ormore objects being assigned a connecting element in which informationfor coordinating the objects is stored.
 4. Method according to claim 3,characterized in that the basic objects or primitive objects areassembled with the aid of Boolean operators from lower geometricalobjects which are produced by rotation, stitching or stretching. 5.Method according to one or more of claims 1 to 4, characterized in thatonly the geometrical shape of individual or a plurality of primitiveobjects is modified.
 6. Method according to one of claims 1 to 5,characterized in that the primitive objects are standardized rasterableobjects such as triangles, rectangles, pentagons, tetrahedra, pentahedraor hexahedra.
 7. Method according to one of claims 1 to 6, characterizedin that the basic objects are, in particular, surfaces, cuboids orrotationally symmetrical bodies.
 8. Method according to one of claims 1to 7, characterized in that each primitive object is assigned aninformation element in which attributes of the primitive object, inparticular parameter values, interval limits and rules, are stored. 9.Method according to claim 1, characterized in that before the rasteringof the primitive objects (step e), the objects are allocatedcoordination elements as additional knowledge.